Browsing by Author "Asmerom, Y"

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    Clumped isotope analysis of Central Australian carbonates: a potential palaeoclimate proxy for Australia’s arid interior
    (American Geophysical Union (AGU), 2022-12-13) Nixon, F; Tyler, JJ; Priestley, SC; Cohen, TJ; Klaebe, RM; Crossey, LJ; Karlstrom, KE; Polak, VJ; Asmerom, Y; Love, AJ; Hua, Q; Wade, B; Pollard, T; Drysdale, RN; Hall, PA
    Quantitative records of past temperature variability in arid environments are crucial for validating climate models and their ability to capture the full range of the Earth’s climatic regions. However, arid zone temperature reconstructions are rare, particularly in the Southern Hemisphere, including Australia. The clumped isotope thermometer provides a novel approach to potentially address this demand by allowing the estimation of carbonate precipitation temperature independent of environmental water isotopic composition. Two types of carbonate materials offer potential for clumped isotope temperature reconstructions in arid central Australia: fossil mollusk shells deposited within the shoreline sediments of now dry lakes, and tufa deposits formed in mound springs fed by continuous discharge of Great Artesian Basin groundwater. Here we present preliminary clumped isotope analyses from tufa and shell samples from central Australia. We also discuss the use of micro-XRF scanning and XRD to evaluate sample suitability for both clumped isotope analysis and U-series dating. Air temperatures inferred from tufa Δ47 measurements suggest mean annual air temperatures (MAAT) ~5°C cooler than present between 12-9 ka, which supports palaeoclimate model based estimates for central Australia. Average air temperatures inferred from mollusk shells indicate MAAT at least 15°C cooler than present during 70-35 ka, suggesting a larger MAAT reduction than previously estimated. Carbonate δ18O appears to have been largely driven by changes in environmental water δ18O for lakes but not for mound springs, reflecting different hydrological controls on the two water sources. Agreement between temperatures and palaeoclimate models suggest clumped isotope analysis may function as a valuable quantitative palaeotemperature proxy in central Australia. Analysis of additional tufa and shell samples along with an investigation of the genesis of different tufa is ongoing.
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    Clumped isotope analysis of central Australian carbonates: a potential palaeoclimate proxy for Australia’s arid interior
    (Australasian Quaternary Association Inc., 2022-12-06) Nixon, F; Tyler, JJ; Priestley, SC; Cohen, TJ; Klaebe, RM; Crossey, LJ; Karlstrom, KE; Polyak, VJ; Asmerom, Y; Love, A; Hua, Q; Wade, B; Pollard, T; Drysdale, RN; Hall, PA
    Quantitative records of past temperature variability in arid environments are crucial for validating climate models and their ability to capture the full range of the Earth’s climatic regions. However, arid zone temperature reconstructions are rare, particularly in the Southern Hemisphere, including Australia. The clumped isotope thermometer provides a novel approach to potentially address this demand by allowing the estimation of carbonate precipitation temperature independent of environmental water isotopic composition. Two types of carbonate materials offer potential for clumped isotope temperature reconstructions in arid central Australia: fossil mollusk shells deposited within the shoreline sediments of now dry lakes, and tufa deposits formed in mound springs fed by continuous discharge of Great Artesian Basin groundwater. Here we present preliminary clumped isotope analyses from tufa and shell samples from central Australia. We also discuss the use of micro-XRF scanning and XRD to evaluate sample suitability for both clumped isotope analysis and U-series dating. Air temperatures inferred from tufa Δ47 measurements suggest mean annual air temperatures (MAAT) ~5°C cooler than present between 12-9 ka, which supports palaeoclimate model based estimates for central Australia. Average air temperatures inferred from mollusk shells indicate MAAT at least 15°C cooler than present during 70-35 ka, suggesting a larger MAAT reduction than previously estimated. Carbonate δ18O appears to have been largely driven by changes in environmental water δ18O for lakes but not for mound springs, reflecting different hydrological controls on the two water sources. Agreement between temperatures and palaeoclimate models suggest clumped isotope analysis may function as a valuable quantitative palaeotemperature proxy in central Australia. Analysis of additional tufa and shell samples along with an investigation of the genesis of different tufa is ongoing.
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    Clumped isotope analysis of central Australian carbonates: a potential palaeoclimate proxy for Australia’s arid interior
    (Australasian Quaternary Association Inc., 2022-12-06) Nixon, F; Tyler, JJ; Priestley, SC; Cohen, TJ; Klaebe, RM; Crossey, L; Karlstrom, KE; Polyak, V; Asmerom, Y; Love, AJ; Hua, Q; Wade, B; Pollard, T; Drysdale, R; Hall, PA
    Quantitative records of past temperature variability in arid environments are crucial for validating climate models and their ability to capture the full range of the Earth’s climatic regions. However, arid zone temperature reconstructions are rare, particularly in the Southern Hemisphere, including Australia. The clumped isotope thermometer provides a novel approach to potentially address this demand by allowing the estimation of carbonate precipitation temperature independent of environmental water isotopic composition. Two types of carbonate materials offer potential for clumped isotope temperature reconstructions in arid central Australia: fossil mollusk shells deposited within the shoreline sediments of now dry lakes, and tufa deposits formed in mound springs fed by continuous discharge of Great Artesian Basin groundwater. Here we present preliminary clumped isotope analyses from tufa and shell samples from central Australia. We also discuss the use of micro-XRF scanning and XRD to evaluate sample suitability for both clumped isotope analysis and U-series dating. Air temperatures inferred from tufa Δ47 measurements suggest mean annual air temperatures (MAAT) ~5°C cooler than present between 12-9 ka, which supports palaeoclimate model based estimates for central Australia. Average air temperatures inferred from mollusk shells indicate MAAT at least 15°C cooler than present during 70-35 ka, suggesting a larger MAAT reduction than previously estimated. Carbonate δ18O appears to have been largely driven by changes in environmental water δ18O for lakes but not for mound springs, reflecting different hydrological controls on the two water sources. Agreement between temperatures and palaeoclimate models suggest clumped isotope analysis may function as a valuable quantitative palaeotemperature proxy in central Australia. Analysis of additional tufa and shell samples along with an investigation of the genesis of different tufa is ongoing.
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    Reply to Comment on “Uranium series dating of Great Artesian Basin travertine deposits: Implications for palaeohydrogeology and palaeoclimate” by Uysal et al. (2019).
    (Elsevier, 2020-01-01) Priestley, SC; Karlstrom, KE; Love, AJ; Crossey, LJ; Polyak, VJ; Asmerom, Y; Meredith, KT; Crow, R; Keppel, MN; Habermehl, MA
    Tonguc Uysal and co-authors (this issue) propose that at least some of the U-series ages reported by Priestley et al. (2018) and Ring et al. (2016) provide minimum ages of movement at the Norwest Fault Zone in central Australia resulting from significant CO2 production due to mantle degassing related to active tectonics. We thank Tonguc Uysal and co-authors for their discussion on the role of tectonics and CO2 degassing in travertine precipitation and note that we had previously published (and agree with) the importance of mantle degassing as a source of CO2 that closely interacts with palaeohydrogeologic and palaeoclimatic forcings in explaining the rate and distribution of travertine deposition in the southwestern Great Artesian Basin (GAB) of central Australia. Based in part on western U.S. analogues (Crossey et al., 2016; Karlstrom et al., 2013a), we proposed and explored a model for these processes and their implications for the GAB in previous publications (Crossey et al., 2013; Karlstrom et al., 2013b) whereas Priestley et al. (2018) focused more specifically on palaeoclimate implications. Crown Copyright © 2019 Published by Elsevier B.V
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    Uranium series dating of Great Artesian Basin travertine deposits: implications for palaeohydrogeology and palaeoclimate
    (Elsevier, 2018-01-15) Priestley, SC; Karlstrom, KE; Love, AJ; Crossey, LJ; Polyak, VJ; Asmerom, Y; Meredith, KT; Crow, R; Keppel, MN; Habermehl, MA
    Travertine deposits precipitated by groundwater discharging from the Great Artesian Basin (GAB) are widespread in central Australia and have the potential to provide a record of palaeohydrogeology and palaeoclimate. The GAB is one of the largest artesian basins in the world and a relationship between travertine deposits and recharge sites has potential importance regarding the time and position of past climate events, given that the travertines growth forms from precipitation discharge. We sampled numerous travertine sites in the southwest section of the GAB as a first approach to test this relationship. U-series dating of the travertine deposits reveal that spring discharge has likely been episodic for the last several hundred thousand years. Spring travertine deposition occurred episodically around 465 ± 50 ka, 370 ± 20 ka, 335 ± 15 ka, 285–240 ka, 185 ± 10 ka, 160–150 ka, 110–100 ka and during the past 30 ka. The periodicity of travertine ages observed with simultaneous deposition at multiple locations, argues for regional palaeohydrologic controls. Comparison of the travertine deposit ages with climate proxies in Australia shows that elevated travertine deposition rates are synchronous with wet periods in both central and southern Australia. Due to the large size of the GAB and that the recharge zones extend over multiple climatic regions of Australia, the times of travertine deposition are interpreted to represent times of high rainfall regionally. This study shows that the travertine deposits of central Australia provide a datable archive of past climate and hydrogeology of importance for understanding the groundwater evolution of the Great Artesian Basin, and that further more comprehensive studies are warranted. © 2018 Elsevier B.V.